It is often desirable to monitor oceanographic conditions remotely using unattended equipment. The data on such conditions is often useful both for military and civilian purposes. This is particularly true when the area from which the data desired is inhospitable or distant or where the data must be gathered over a long period of time. Such difficult conditions often occur in the arctic and antarctic regions.
A number of methods have been used to remotely monitor oceanographic conditions with automated equipment. The most commonly used arrangement is to moor a cable to an anchor on the seafloor. The cable may be held upright by a surface float(s) or subsurface float(s). On the cable are mounted current meters or devices to measure ocean temperature, conductivity, (for salinity determination), or other variables. These instruments record data internally and the mooring must be recovered from the ocean in order to obtain the data at the end of the experiment. Typically data are not available on a real-time basis during the experiment and if through acts of nature or equipment malfunction, the mooring cannot be recovered, all the data are lost. In ice covered regions such bottom moorings are very difficult to recover. A common innovative technique for experiments has been to hang moorings from the drifting sea ice.
In order to overcome the deficiencies of internally recording instruments it has become a common practice to telemeter data back to shore by HF radio link or via VHF satellite link such as the ARGOS system. This approach is especially useful in ice covered regions when use of a surface buoy makes radio transmission convenient and where recovery to the instruments is often impractical. This technique is described in an article entitled SALARGOS Temperature-Conductivity Buoys, published in the September 1982 issue of Oceans pp 1255-1260. The telemetry technique can be used in the open ocean if a surface float is used or if a companion surface float is attached to an array of subsurface floats.
The simplest and most common arrangement for the measurements on one of these vertical oceanographic arrays is to attach individual sensors at fixed depths on the cable, even when the data are collected and transmitted to some surface module. The problems with this approach are twofold. In order to measure over a large vertical extent, many sensors must be used and this adds to the cost of the array. Even with a large number of sensors, the vertical resolution of the measurements is limited by the vertical separation between sensors. One way to overcome these cost and resolution problems is somehow to move a single sensor up and down the mooring cable. The technical difficulties with this approach are to provide the power to move the sensor package and, if it is desired to telemeter the data, to transmit data from the moving sensor package to the surface. Providing power to move the sensor package is especially difficult if instrument size is to be constrained and it is desirable to operate the instrument for a long period of time without attention.
Profilers have been proposed that use gas stored at high pressure which is used to control buoyancy in ballast tanks or pump fluid into an external bladder to change buoyancy. Because these devices use stored energy they are too large and too limited in endurance to be practicable for long-term use in ice covered seas. The device described here should achieve long endurance and small size in two ways. First, by not using stored energy but rather by extracting energy for vertical motion from ocean currents. And second, by minimizing the force required for vertical motion by maintaining near neutral buoyancy over a wide range of water depths.
The profiler should not only move a sensor package up and down but also inherently act as a profiling current meter. The device should be suitable in either ice-covered or ice-free seas.